diff --git a/collects/macro-debugger/model/deriv-c.ss b/collects/macro-debugger/model/deriv-c.ss
index 1e54bebddd..09eea0eff0 100644
--- a/collects/macro-debugger/model/deriv-c.ss
+++ b/collects/macro-debugger/model/deriv-c.ss
@@ -58,12 +58,12 @@
 ;;   (make-p:#%expression <Base> Deriv ?Stx)
 ;;   (make-p:if <Base> Boolean Deriv Deriv Deriv)
 ;;   (make-p:wcm <Base> Deriv Deriv Deriv)
-;;   (make-p:set! <Base> Rs Deriv)
+;;   (make-p:set! <Base> Rs ?Exn Deriv)
 ;;   (make-p:set!-macro <Base> Rs Deriv)
 (define-struct (p:#%expression prule) (inner untag) #:transparent)
 (define-struct (p:if prule) (test then else) #:transparent)
 (define-struct (p:wcm prule) (key mark body) #:transparent)
-(define-struct (p:set! prule) (id-resolves rhs) #:transparent)
+(define-struct (p:set! prule) (id-resolves ?2 rhs) #:transparent)
 (define-struct (p:set!-macro prule) (deriv) #:transparent)
 
 ;;   (make-p:#%app <Base> Stx LDeriv)
diff --git a/collects/macro-debugger/model/deriv-parser.ss b/collects/macro-debugger/model/deriv-parser.ss
index 17c14f5875..7bb6d7b4f7 100644
--- a/collects/macro-debugger/model/deriv-parser.ss
+++ b/collects/macro-debugger/model/deriv-parser.ss
@@ -486,8 +486,9 @@
 
     (PrimSet
      (#:args e1 e2 rs)
-     [(prim-set! ! Resolves next (? EE))
-      (make p:set! e1 e2 rs $2 $3 $5)]
+     ;; Unrolled to avoid shift/reduce
+     [(prim-set! ! resolve Resolves ! next (? EE))
+      (make p:set! e1 e2 rs $2 (cons $3 $4) $5 $7)]
      [(prim-set! Resolves (? MacroStep) (? EE))
       (make p:set!-macro e1 e2 rs #f ($3 e1 $2 $4))])
 
diff --git a/collects/macro-debugger/model/reductions.ss b/collects/macro-debugger/model/reductions.ss
index c5fe47ba06..3cd9fa8308 100644
--- a/collects/macro-debugger/model/reductions.ss
+++ b/collects/macro-debugger/model/reductions.ss
@@ -235,10 +235,11 @@
      (R [! ?1]
         [#:pattern ?form]
         [Expr ?form deriv])]
-    [(Wrap p:set! (e1 e2 rs ?1 id-rs rhs))
+    [(Wrap p:set! (e1 e2 rs ?1 id-rs ?2 rhs))
      (R [! ?1]
         [#:pattern (?set! ?var ?rhs)]
         [#:learn id-rs]
+        [! ?2]
         [Expr ?rhs rhs])]
 
     ;; Macros